At a time when ten states and Washington D.C. have legalized adult-use cannabis and more than thirty have medical cannabis laws, there is rising concern in the American medical community that more pregnant mothers may use cannabis. Doctors also worry that there’s a growing perception it’s not harmful. For example, a 2015 study in the American Journal of Obstetrics and Gynecology found that 70% of pregnant and nonpregnant woman believe that there is slight or no risk to using marijuana once or twice a week.

A study of pregnant women at the Kaiser Permanente healthcare system in California, meanwhile, found that usage of the drug increased from 4 percent in 2009 to 7 percent in 2016. Roughly 22 percent of pregnant females under 18, and 19 percent of pregnant females age 18 to 24, screened positive for marijuana in 2016, the study found.

What are the dangers? In fact, there have been few studies done on cannabis use in expectant mothers, compared to the breadth of research on tobacco and alcohol usage during pregnancy. Yet some that have been done have raised concerns.

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One long-term study that has gained attention was published in September 2018 in the International Journal of Epidemiology. It found that cannabis use during pregnancy could be associated with behavioral problems in children.

The study—of more than 5,900 children in the Netherlands—found that kids who had been exposed to cannabis as fetuses during pregnancy exhibit more behavioral issues, like rule breaking or aggression. The findings are part of larger longitudinal study called Generation R, which is observing the growth and development of 10,000 children from birth to young adulthood in Rotterdam.

To isolate cannabis exposure, the researchers in the Netherlands examined and compared several non-overlapping groups of parents: pregnant women who used cannabis, women who used cannabis before pregnancy only, pregnant women who smoked tobacco only, and non-using pregnant women. The researchers had expectant mothers self-report cannabis use and also tested urine samples for THC.

Hanan El Marroun, an assistant professor in the Department of Child and Adolescent Psychiatry at Erasmus Medical Center, and the lead author on the study, said the group used a standardized questionnaire to examine emotional and behavioral issues in children age seven to ten, which was reported by their teachers and mothers. “Behavior problems include, for example, aggressive behavior or rule-breaking behavior while emotional problems include, for example, being withdrawn, anxious, or depressed,” Marroun told Cannabis Wire. The kids were also asked to self-report any problems at age nine.

The researchers found that children whose mothers or fathers used cannabis during pregnancy scored higher on a scale for behavioral problems. At the same time, they also found that tobacco use during pregnancy was also associated with behavioral issues, a finding that has been echoed in other studies.

It is unlikely that intrauterine cannabis exposure alone causes behavioral problems, the researchers said. It is probable that otherfamilial factors, like genetics,also play a role. “Studying the effects of cannabis use on child development is very complex,” Marroun added.

Yet other studies mirror these findings. Two long-term studies, the Ottawa Prenatal Prospective Study at Carleton University, and the Maternal Health Practices and Child Development study at the University of Pittsburgh, also looked at cannabis exposure in utero, and both suggest that it could be associated with behavioral problems in kids. The studies found that such cannabis use could be linked to increased hyperactivity and impulsivity in early childhood, as well as memory problems. Adolescents in these long-term studies showed increased risk of depression and delinquent behavior, such as drug use.

The Generation R researchers in the Netherlands agree that more work needs to be done to fully understand the impact cannabis use can have on children during pregnancy. “Future studies with repeated assessments of parental psychopathology and substance use before, during and after pregnancy will be needed to address this,” they wrote.

State Senator Diane Savino tells Cannabis Wire that legalization could be stalled for three years, and that “unless something changes within the next 36-48 hours, we will miss the opportunity to make New York the next state to adopt an adult use program.”